1. Field of the Invention
The invention relates generally to video games, and more specifically, to video games that employ a playfield that scrolls relative to a game character in order to show character motion through the playfield.
2. Description of the Related Art
Video games are well known in which a game character, or sprite, follows a prescribed path through a scrolled playfield in response to the commands of a user who is playing the game. The user operates an input device which includes a control console which may include a "joy stick" used to control character movement. A user command issued through the input device for the character to move right results in the playfield scrolling to the left which creates the impression that the character is moving to the right relative to the playfield. Conversely, a user command for the character to move left results in the playfield scrolling to the right which creates the impression that the character is moving to the left. During such scrolling the character image ordinarily remains fixed near the center of the screen display despite the appearance of movement relative to the playfield.
In typical video games, the input device permits the user to command the character to perform numerous activities such as to jump or to crouch down or to speed-up or to slow-down. Often, a game character takes on different appearances as it engages in different activities. For example, when the character moves at slower speeds, its legs, arms and torso may be fully visible as the playfield scrolls slowly. However, when the character speeds up, most of the character image may be portrayed as a blur with only the character head being fully recognizable while the playfield scrolls rapidly. Moreover, the character may have one portrayal when it crouches and another portrayal when it jumps. Additionally, there may be special character antics that involve a series of images, such as tumbling, throwing a kick or "flying" through the air.
A challenge associated with implementing such video games is to produce a playfield which has a variety of images and obstacles. For example, there may be mountains to climb, canyons to jump over or enemies to defeat. In the midst of all of this activity, changes in the appearance and movements of the character and the playfield must occur smoothly and quickly so as not to distract the user or detract from the excitement of a high speed action packed video game.
Consequently, certain uniform techniques often are employed to control the movement and appearance of game characters and the playfield. These techniques include defining a path to be followed by the character through the playfield. The character moves along the path in response to user commands. For example, if the path ascends to the right, and the user commands the character to move to the right, then the character is depicted climbing the path to the right as the playfield scrolls to the left. If the user subsequently commands the character to move back towards the left, then the character will be shown descending the path to the left as the playfield scrolls to the right.
The image of the character moving along the path is produced under the control of a computer program. Character movement is constrained by the program such that as the character moves left or right, it always tries to maintain contact with the path. If the character jumps, for example, it soon returns (falls) to the path. If the path includes a discontinuity such as an on-screen image of a cliff, for example, then a character running off the edge of the cliff might fall to another path at the base of the cliff; or it might jump across the chasm at the edge of the cliff and land on a path opposite the cliff. The user controls character movement, but the program ensures that the character generally follows the path.
While paths through the playfield generally have been an acceptable way to constrain character movement, there have been shortcomings with there use. For example, a typical earlier method for making sure that a character follows the path is to use collision blocks. As the character moves in response to user commands, a computer program references stored collision blocks to determine the exact path to be followed in response to such commands. Specifically, the playfield is divided into graphics blocks. As the character traverses individual graphics path blocks, a path control program references individual collision blocks that correspond to such graphics path blocks. A collision block is used to determine, for example, whether the path within a graphics path blocks is level, inclined or drops off a cliff.
A problem associated with such earlier methods is that it may be desirable to define two different paths through the same region of a graphics path block. Unfortunately, a collision block typically defines only a single path, and each graphics path block corresponds to only one collision block. Therefore, it has been difficult to provide multiple paths through the same region of a graphics path block.
Thus, there has been a need for improved techniques which permit multiple paths through the same region of a graphics path block. The present invention meets these needs.